In many parts of the world due to inadequate rainfall it is necessary at certain times during the year to artificially water turf and landscaping. An ideal irrigation system for turf and landscaping should utilize a minimum number of valves, supply lines and sprinklers. Preferably the valves should be turned ON and OFF by an inexpensive, yet reliable electronic irrigation controller that is easy to program and can carry out a wide variety of watering schedules. The goal is to uniformly distribute the optimum amount of water over a given area. The type, placement and flow rates for each of the sprinklers are pre-selected when an irrigation system is designed and/or installed. The optimum flow rate provided by each sprinkler should preferably fall within plus or minus one-quarter gallon-per minute (GPM). The amount of water supplied by each sprinkler is largely determined by the size and configuration of its nozzle orifice(s), although variations result from fluctuations in water pressure that cannot be fully negated with regulators.
Residential and commercial irrigation systems typically include one or more solenoid operated valves that are turned ON and OFF by the electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone. A modern electronic irrigation controller typically includes a microprocessor that executes one or more watering programs. The watering programs can, typically, be pre-programmed by the user via push button and/or rotary controls. The watering programs contain one or more watering schedules which consist of run and cycle times for each station. The controller usually has an LCD or other display to facilitate programming by the user. Often the controller will revert to a default watering program in the case of a power failure. The microprocessor controls the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Homeowners, conservationists and water purveyors are increasingly interested in minimizing the amount of water used for irrigation, especially in areas where water is in short supply. Some municipalities have enacted restrictions on residential and commercial watering. While such restrictions do save water, they are often arbitrary and do not take into account the watering needs of different types of vegetation in different geographic locations. Techniques have been developed for tailoring watering schedules in an electronic irrigation controller to accommodate different kinds of plants and atmospheric conditions based on evapotranspiration (ET) rate. This is a number that represents the amount of water lost by a plant via evaporation and also the amount of water lost by the plant through transpiration, i.e. loss of water through its leaves. See for example U.S. Pat. No. 5,097,861 granted Mar. 24, 1992 to Hopkins et al. and assigned to Hunter Industries, Inc. of San Marcos, Calif., which discloses a controller that utilizes stored historic ET data for each zip code, along with other stored data, to calculate watering schedules.
The primary environmental factors needed to calculate ET are temperature, amount of solar radiation, relative humidity and wind speed. Rainfall is not included because it is only a source of water and has little effect on how quickly plants lose water. However, an irrigation controller should take into account the effective rainfall, via rain interrupt sensor or otherwise, in determining the optimum watering schedule. Effective rainfall depends upon such things as soil type, slope and root depth as these determine the amount of water that actually makes it to the plant roots as opposed to the amount of runoff. Atmospheric conditions affect both evaporation and transpiration. Plant type also affects transpiration.
Conventional techniques for using ET data in an irrigation controller often require a fee to be paid for receiving and utilizing the ET information. Irrigation controllers capable of calculating watering schedules based on ET are typically complicated to use and expensive to buy. Those schedulers which “piggy back” onto an existing controller have limitations because they can only reduce the existing watering schedules in the base controller.